The invention relates to a pilot device including a pressure-displacement transducer in which a difference in pressure between a pressurized space and another space separated therefrom can be converted into a movement of an adjusting body, a pilot part to be triggered by the adjusting body for activating a safety valve of a pressure vessel, a pressure-removal line for connecting the pressure vessel to the pressurized space, and a drainage line for connecting the other space to a blow-off tank.
German Published, Non-Prosecuted Patent Application DE 39 06 888 A1 and German Patent DE 196 28 610 C1 disclose pilot devices for activating a safety valve. The pilot devices in those cases are spring-loaded pilot valves, i.e. pilot valves which operate in accordance with the closed circuit principle. They have a valve spring which acts counter to a hydraulic force derived from a system pressure of a system which is to be protected, for example a pressure vessel. Pilot valves of that type are therefore actuated solely by the system pressure which means that external energy does not necessarily have to be supplied by motor-driven, magnetic, pneumatic or hydraulic devices, for example.
At least three lines emerge from a pilot valve in the above-mentioned publications: a first line is a pressure-removal line (measuring line) through the use of which the pilot valve can be acted upon by the system pressure in the pressure vessel. A second line is a control line through which the pilot valve acts upon the safety valve. For example, in order to open a safety valve operating in accordance with the discharging principle, the safety valve is discharged through the control line. A third line is a drainage line (blow-out line) which either leads into the atmosphere or opens into a blow-off tank (pressure-maintaining blow-off tank), especially in the case of nuclear power plants. For example, a safety valve operating in accordance with the discharging principle is discharged into the blow-off tank through the control line and the drainage line.
In order to actuate, i.e. to trigger, the above-mentioned pilot devices, a pressure-displacement transducer is provided in which a difference in pressure between a pressurized space and another space separated therefrom can be converted into a movement of an adjusting body. The pressure-removal line opens into the pressurized space. The pressure-displacement transducer of German Published, Non-Prosecuted Patent Application DE 39 06 888 A1 has a transducer piston which is guided in a cylinder and can be acted upon by the pressure in the pressurized space. The pressure-displacement transducer of German Patent 196 28 610 C1 is equipped with a transducer bellows having an interior which forms the pressurized space. In both cases, the difference in pressure between the pressurized space and the other space in the pressure-displacement transducer is converted into a movement of the adjusting body. The adjusting body is formed, in particular, by the transducer piston or by a bellows head of the transducer bellows. The adjusting body acts through a tappet on a pilot part which, for example, triggers the discharging of a safety valve operating in accordance with the discharging principle. The pilot part of German Patent DE 196 28 610 C1 includes a xe2x80x9cprepilot partxe2x80x9d and a xe2x80x9cpilot partxe2x80x9dacting directly on the safety valve.
In cases in which the other space is connected to the drainage line opening into the blow-off tank, the above-mentioned pilot valves are disadvantageously sensitive to a rise in pressure in that blow-off tank. A short-lived but strong rise in pressure could, for example, be produced in that tank if, in the event of a fault, the pressure in the blow-off tank exceeds the design value, thereby causing a bursting membrane serving to protect the pressure of the blow-off tank to break. A rise in pressure of that type could lead to an undesired, premature closing of an open, i.e. blowing-off, safety valve. However, even a relatively small rise in pressure in the blow-off tank can have disadvantageous effects on the functioning of the pilot valve. That is because, as a result, the response pressure for opening the activated safety valve can be markedly changed through the drainage line. A rather small rise in pressure of that type in the blow-off tank can be caused, for example, by the blowing-off of a safety valve if the blowing-off takes places through a blow-off line into the blow-off tank, as is customary in nuclear power plants. Even a safety valve blowing off at that time could therefore disadvantageously change the response pressure of another safety valve which is still closed.
It is accordingly an object of the invention to provide a pilot device for a safety valve, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type, which is insensitive to a rise in pressure in a blow-off tank and in which, in particular, an undesired closing of an open safety valve or an effect on a response pressure for opening a safety valve through the use of a rise in pressure in the blow-off tank, is reliably avoided.
With the foregoing and other objects in view there is provided, in accordance with the invention, a pilot device, comprising a pressure-displacement transducer having a pressurized space, another space separate from the pressurized space, and an adjusting body, for converting a difference in pressure between the pressurized space and the other space into a movement of the adjusting body; a pilot part to be triggered by the adjusting body for activating a a safety valve of a pressure vessel; a pressure-removal line for connecting the pressure vessel to the pressurized space; a blow-off tank; a drainage line for connecting the other space to the blow-off tank; and a switchcover valve device associated with the drainage line and having an outgoing take-off line, the switchcover valve device connecting the other space to the take-off line instead of to the blow-off tank when a pressure in the blow-off tank is above a limiting pressure.
In the case of this pilot device according to the invention, an excessive pressure in the blow-off tank is kept away from the pressure-displacement transducer. It is ensured at the same time that fluid can flow out of the other space through the take-off line. The take-off line can open, for example, into a nuclear power plant draining system which is always unpressurized.
The switchover valve device can, for example, be disposed at least partially in the drainage line. The take-off line can branch off from the drainage line through the switchover valve device.
In accordance with another feature of the invention, the switchover valve device includes a drainage valve device which is disposed in the drainage line and a take-off valve device which is disposed in the take-off line.
In accordance with a further feature of the invention, the drainage valve device and/or the take-off valve device is/are closed in a starting position of the adjusting body in which the pilot part is not triggered. This ensures that the other space is isolated from the blow-off tank during normal operation. Normal operation means that the safety valve is closed, i.e. that in the case of a safety valve operating in accordance with the discharging principle, no fluid flow (drainage) can be taken off out of the pilot device.
In accordance with an added feature of the invention, the closing force of the drainage valve device is smaller than a closing force of the take-off valve device.
During implementation of the discharging principle, fluid (drainage) flowing out of the pilot part, when the pilot part is triggered, passes through the drainage line to the switchcover valve device. As a result, the pressure at the drainage valve devices rises, the drainage valve device opens and the fluid can be blown out into the blow-off tank through the drainage line. After a rise in pressure in the blow-off tank, it is not possible to open the drainage valve device or else the drainage valve device closes again because of this rise in pressure. In this case, the take-off valve device opens after the pressure upstream of the switchcover valve device has risen slightly further because of the further flowing out of fluid. The fluid can then be blown out through the take-off line.
With the objects of the invention in view, there is also provided a pilot device, comprising a pressure-displacement transducer having a pressurized space, another space separate from the pressurized space, and an adjusting body, for converting a difference in pressure between the pressurized space and the other space into a movement of the adjusting body; a pilot part to be triggered by the adjusting body for activating a safety valve of a pressure vessel; a pressure- removal line for connecting the pressure vessel to the pressurized space; a blow-off tank having a given pressure; a drainage line for connecting the other space to the blow-off tank; a compensating line; and a hydraulic compensating system to be connected to the blow-off tank through the compensating line, the hydraulic compensating system producing a first force on the adjusting body from the given pressure, and the first force counteracting a second force on the adjusting body produced in the other space by the given pressure.
As a result, the undesirable second force does not have an effect, or at least does not have a severe and undesirable effect, on the pressure-displacement transducer. In contrast to the first embodiment, the second embodiment affords the additional advantage that an active flowing-out of fluid (drainage) into a space outside the blow-off tank does not occur.
With regard to both embodiments according to the invention, a pressure-displacement transducer is understood to be any system in which a change in pressure, in particular a rise in pressure, can be converted into a positional change of an adjusting body. That occurs irrespective of whether the positional change takes place continuously with increasing pressure or abruptly at a certain limiting pressure.
The safety valve of one of the two embodiments can operate in particular in accordance with the discharging or loading principle. Activation through the use of the pilot part leads to discharging or loading and therefore to the opening of the safety valve.
In accordance with another feature of the invention, the adjusting body in one of the two embodiments is connected to a transducer piston and/or to a first transducer bellows, which piston and/or bellows can be acted upon by the pressure in the other space and can be used to produce the second force.
In accordance with a further feature of the second embodiment of the invention, the hydraulic compensating system includes a compensating piston and/or a compensating bellows which can be acted upon by the pressure in the blow-off tank, and which can be used to produce the first force. The first force can, in particular, be transmitted mechanically from the compensating piston or from the compensating bellows to the adjusting body.
In accordance with an added feature of the invention, the diameter of the compensating piston and/or of the compensating bellows essentially corresponds to the diameter of the transducer piston and/or of the first transducer bellows. In the case of a refinement of this type, a rise in pressure in the blow-off tank has virtually no effect on the functioning of the pressure-displacement transducer. As in the case of a pilot device without a hydraulic compensating system, an increased pressure in the blow-off tank produces the undesirable second force on the adjusting body. However, since the other space is connected to the blow-off tank through the drainage line, this pressure at the same time also acts on the compensating piston or the compensating bellows and thereby produces the first force on the adjusting body. That force compensates for the undesirable second force.
In accordance with an additional feature of the invention, the compensating piston and the compensating bellows are disposed in such a way that they can move along an axis along which the adjusting body can also be moved. This ensures that the first force which is produced at the compensating piston and the compensating bellows can be transmitted in a simple and reliable manner to the adjusting body.
In accordance with yet another feature of the invention, the compensating piston and the compensating bellows are disposed in series with the adjusting body. Such a configuration one behind another in a straight line has the advantage of permitting the hydraulic compensating system to be retrofitted simply and rapidly onto an existing pilot device which does not have a hydraulic compensating system.
In accordance with yet a further very particularly preferred feature of the invention, the compensating piston or the compensation bellows is disposed in such a way that it at least partially surrounds the transducer piston or the first transducer bellows or a second transducer bellows. This enables the hydraulic compensating system to be integrated in a particularly space-saving and compact manner in the control device for the safety valve.
In accordance with yet an added feature of the invention, the compensating piston or compensating bellows has an undergrip-like driver for the transducer piston or for one of the transducer bellows.
In accordance with yet an additional feature of the invention, the drainage line and/or the compensating line is laid on a slope, as seen from the hydraulic compensating system. This provides the advantage of enabling pressure medium, for example condensate, which has penetrated to flow out of the control device again, in particular after the buildup of pressure has finished.
In accordance with a concomitant feature of the invention, the first force is transmitted, for example through the use of the driver, to the transducer piston or to one of the transducer bellows and is transmitted to the separate adjusting body, if the piston or bellows do not themselves form the adjusting body.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a pilot device for a safety valve, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.